2. The second prop is a cup and coaster: there is a white column in the middle of the cup base, which is a hollow tube with a switch inside. A coaster is like a small quilt, which is filled with a strong hygroscopic substance. The straw also has the function of starting the switch: Liu Yi sucks the straw, the switch is turned on, and the coffee flows downwards; Liu stopped sucking straws, turned off the switch, and the coffee stopped flowing downwards.